Local wall shape, principal fiber-path directions and curvatures will be mapped in the left and right ventricles and atria of autopsy hearts. The entire heart will be encapsulated in 10 percent gelatin, hardened by refrigeration, then sectioned in a miter box equatorally through the LV/RV equator and longitudinally on the prime meridianal plane bisecting LV and RV. Orthogonally oriented fiducials will be permanently inserted into each of 2 LV free-wall, 2 septal, 3 RV free-wall, 3 LA and 3 RA sites prior to excision of through-wall blocks containing them. X-Y coordinates of local wall shape and fiducial dimensions will be recorded manually or by X-Y digitizer. Using the innovative "rotated sections" method of sectioning of a prestained paraffin block, we will obtain through-wall sections at a regular sequence of alpha 1 angles (the helix angle component of a fiber path in a plane parallel to the local epicardium). On each section, stained with a trichrome stain, we will record by light microscopy and X-Y digitizer the location of the in-plane fiber paths and their direction beta (the imbrication angle component, which measures the extent to which the fiber paths depart from the direction of the epicardial tangent). Using standard graphics software and display equipment we will generate 3-dimensional perspective plots of principal-fiber pathways in the LV, RV, LA and RA walls that will facilitate comparisons of normal to abnormal myocardium. These pathways will also be used to depict the spread of the wave of depolarization through the wall.